The mechanism of enzymic catalysis and its control will be studied by equilibrium kinetics utilizing isotopic exchange of subtrates and other techniques. BIBLIOGRAPHIC REFERENCES: Skarstedt, M. T. and Silverstein, E. Magnesium, nucleotide and substrate interactions reflected in equilibrium, initial net rate and isotopic exchange kinetics of Escherichia coli acetate kinase. Fed. Proc. 34:3, 496 (no. 1555) 1975; Kim, G. and Silverstein, E. Development change in guanyl cyclase and cyclic 3'5' guanosine monophosphate in the rat lung and heart. Fed. Proc. 34:3, 231 (no. 74) 1975.